He said: "We would have loved to keep him. We would have loved to keep Jessica [Brown Findlay, who played Lady Sybil Crawley] too.

"We have always tried to persuade him to stay. He had done fantastically well for the series and his creation of Matthew was terrific.

"But this is life. Dan felt that this was right thing for him, and the right moment to move on to different areas."

The screenwriter said that he would have been open to keeping Matthew alive if Stevens agreed to guest appearances in future, but the actor was adamant that he wanted to move on from the role.

"If he had been prepared to come back for maybe two or three episodes in a series, that would be different. Then we could have had a foreign posting or invented a career that would have made it possible for him to be away," Fellowes explained.

"Otherwise we would have had to make this tremendously successful love affair between Mary and Matthew unhappy, which I didn't feel would be believable.

"For them to then separate and Matthew never set eyes on his son again would not be believable either."

He added: "We didn't really have any option. By him dying, their love can remain in tact."